OBJECTIVES FOR THE -18 YEAR: (1) to extend our flavin studies to flavoproteins, (2) to find the pathway for conversion of glucose to ribose, and (3) to study amebal iron-sulfur proteins other than amebal ferredoxin. GOALS FOR THE -19 YEAR: Only objective (2) was fully achieved during the -18 year. For the -19 year we expect to continue studies on (1) and (3) above, and to explore the mechanism by which E. histolytica consumes O2 to form water instead of H2O2. DESCRIPTION OF STUDIES DURING THE YEAR: E. histolytica was found to lack the enzyme transaldolase. In the absence of this enzyme a novel pathway for pentose-hexose interconversion was discovered. This pathway involves amebal transketolase, aldolase, and the reversible PPi-dependent phosphofructokinase. A manuscript embodying these findings has been written and will soon be submitted to a journal. Further work was done on the previously mentioned NADPH:flavin oxidoreductase. This appears to be the first amebal enzyme to be purified to homogeneity. A manuscript describing these results has been submitted to a journal. Exploratory work was done on amebal nucleic acid growth requirements which resulted in a publication. In this laboratory we have tried and failed to confirm published work (Takeuchi, Weinbach and Diamond, Comp. Biochem. and Physiol. (1979) vol. 62B, p. 281-285) relating to a significant role for the amino acid serine in amebal metabolism. It is anticipated that further work will be required along this line.